The present invention relates to new, vaporizable chelate complexes of calcium, barium and strontium, to a method for their synthesis, to their use for depositing layers containing calcium, barium or strontium and to intermediates for synthesizing the compounds.
Metal-organic chemical vapor deposition (MOCVD) is a method, which can be used very well for depositing layers containing metal or metal compounds. It is the method of choice for depositing ceramic thin-layers for a plurality of electronic components. Examples are ferroelectric layers based on barium titanate or barium strontium titanate. Such layers are used, for example, for DRAM components.
For this application, as well as for other applications, it is desirable that the organometallic alkaline earth compounds have a high volatility, which facilitates sublimation and the transport to the place of deposition, that they can be decomposed thermally at relatively low temperatures, such as those of the order of 450° C., and that, for certain application areas, they are deposited in the form of the oxides and not, for example, in the form of other decomposition products such as carbonates.
Alkaline earth metal beta-diketonates and certain derivatives have already been used for the MOCVD method. Classical examples are complexes of alkaline earth metals with 1,1,6,6-tetramethylheptanedionate. However, such complexes may be present as oligomers, the volatility and stability of which are unsatisfactory. In order to improve these properties, the tetramethylheptane dionate complex compounds were used in the form of Lewis base adducts, for example, as adduct with polyethers or polyamines. Such complexes, however, still have stability problems. Barium compounds and strontium compounds with ligands, which have three coordination sites, have also been proposed.